The catecholamine biosynthetic enzyme dopamine β-hydroxylase (DBH): first genome-wide search positions trait-determining variants acting additively in the proximal promoter

Abstract

Dopamine beta-hydroxylase (DBH) is the biosynthetic enzyme catalyzing formation of norepinephrine. Changes in DBH expression or activity have been implicated in the pathogenesis of cardiovascular and neuropsychiatric disorders. Genetic determination of DBH enzymatic activity and its secretion are only incompletely understood. We began with a genome-wide association search for loci contributing to DBH activity in human plasma. Initially, in a population sample of European ancestry, we identified the proximal DBH promoter as a region harboring three common trait-determining variants (top hit rs1611115, P = 7.2 × 10(-51)). We confirmed their effects on transcription and showed that the three variants each acted additively on gene expression. Results were replicated in a population sample of Native American descent (top hit rs1611115, P = 4.1 × 10(-15)). Jointly, DBH variants accounted for 57% of DBH trait variation. We further identified a genome-wide significant SNP at the LOC338797 locus on chromosome 12 as trans-quantitative trait locus (QTL) (rs4255618, P = 4.62 × 10(-8)). Conditional analyses on DBH identified a third genomic region contributing to DBH variation: a likely cis-QTL adjacent to DBH in SARDH (rs7040170, P = 1.31 × 10(-14)) on chromosome 9q. We conclude that three common SNPs in the DBH promoter act additively to control phenotypic variation in DBH levels, and that two additional novel loci (SARDH and LOC338797) may also contribute to the expression of this catecholamine biosynthetic trait. Identification of DBH variants with strong effects makes it possible to take advantage of Mendelian randomization approaches to test causal effects of this intermediate trait on disease.

Figure 1.

Results of the GWAS of plasma DBH activity in 341 subjects of European origin. (A) Manhattan plot showing the −log₁₀ (P-values) for SNP associations with plasma DBH activity across the genome. The red horizontal line represents the genome-wide significance threshold at P < 5 × 10⁻⁸ and the dashed line represents suggestive evidence for association at P < 5 × 10⁻⁶. (B) Regional association plot, showing significant regions in DBH on chromosome 9. Directly genotyped SNPs are indicated by an asterisk (*). The SNPs are color coded based on the linkage disequilibrium with the most significant SNP rs1611115.

Figure 2.

In vitro effects of human DBH promoter variant C-2734T (rs1076150): Balanced mutants on two haplotype backgrounds (HAP2, HAP4) yield consistent (C > T) effects on transcription in chromaffin cells. Strength of the promoter variants is shown as luciferase activity in PC12 cell type (mean ± SEM). P-values are result of C versus T variant comparison for each haplotype background by ANOVA.

Figure 3.

In vivo effects of DBH promoter functional variants T-2734C (rs1076150), C-2073T (rs1989787) and C-970T (rs1611115) on plasma DBH activity (IU/l). (A) DBH promoter diploid haplotype (rs1076150 → rs1989787 → rs1611115) effect on pDBH activity (IU/l). Only subjects homozygous for a given haplotype (rs1076150 → rs1989787 → rs1611115) are shown. (B) Effect of DBH promoter haplotype (rs1076150 → rs1989787 → rs1611115) copy number (0, 1, or 2 copies per genome) on pDBH activity (IU/l, adjusted mean ± SEM).